Ozone Utilization Rate Research Articles

Mechanism of ozone catalysis by transition metal hydroxyl oxides: From reactive oxygen species to surface structural hydroxyl

Transition metal hydroxyl oxides have been used widely as ozone catalysts for water purification. However, the fabrication methods selected and the pollutants treated vary, making it difficult to compare their performance. In this study, ZnOOH, FeOOH, CoOOH, and MnOOH were synthesized by the same method to remove multiple structurally similar targets. Results showed that the ZnOOH performed the best, removing over 90% of all targets within 40min, and presenting the highest ozone utilization rate of 0.081min-1. Multiple ROS quantification and contribution experiments jointly demonstrated that ZnOOH had an advantage over the other catalysts only in ·OH generation, but the ·OH contributed 93% of target removal in the ZnOOH/O3 process. Structure analysis of ZnOOH suggested that its ·OH generation had little connection with the contents of surface metal and adsorbed water, but was dependent on the surface structural hydroxyl that would undergo loss at 100-300℃. This concentration of ZnOOH was 10.1mM/g, which was 1.7, 5.3, and 6.3 times higher than that of FeOOH, CoOOH, and MnOOH, respectively. Heat treatment further revealed that these surface hydroxyl mainly originated from the hydroxyl ions from water dissociation and could regenerate timely during reuse. Finally, a possible catalysis pathway was proposed.

Degradation of clofibric acid by ozonation assisted by Co-Ce-SBA-15: Role of interfacial electron migration

Restrained by the sluggish Ce redox cycle, Ce-SBA-15 exhibited the low electron transfer toward O3 activation. To this end, cobalt‑cerium co-doped SBA-15 with three-dimensional pore structure was designed using urea-assisted hydrothermal method and its activity was evaluated using Clofibric acid (CA) as target pollutant. XRD and N2 adsorption-desorption characterizations suggested that Co-Ce-SBA-15 possessed a three-dimensional pore structure with high order degree. py-FTIR, O2-TPD, H2-TPR, and in situ electrochemical characterizations indicated that compared with Ce-SBA-15 and Co-SBA-15, Co-Ce-SBA-15 had greater Lewis acid strength, electron transfer ability and oxygen reducibility. Co-Ce-SBA-15/O3 achieved the greater CA removal and mineralization rate, with 98.7 % CA removal and 58.3 % TOC removal were obtained in 90 min. Co-Ce-SBA-15/O3 process would be inhibited by the coexisting Cl−, NO3− and SO42−. Co-Ce-SBA-15 demonstrated the greater ozone utilization rate than those of monometallic SBA-15. Lewis acidic sites of Co and Ce were the main sites for activating O3. DFT results suggested that the obvious electron transfer existed among O3, Co and Ce Lewis acid sites. The conversion of Co3+/Co2+ and Ce4+/Ce3+ accelerated the interfacial electron transfer, which favored for conveying O3 into •OH. •OH was the primary reactive oxygen species involved in degrading CA. 8 kinds of intermediates were found during CA degradation and the possible degradation route was proposed. This study deepened the understanding of the cooperative effect of Co and Ce in catalytic ozonation process.

Ultrasound catalytic ozonation to remove 5-hydroxy-1,3-phthalic acid from strongly alkaline and high-salt solutions: Aiding nuclear waste disposal and human health

As a typical precipitation inhibitor and the main component of plasticizers, 5-hydroxy-1,3-phthalic acid (5-HPA) seriously threatens the nuclear waste disposal and human health. OH, 1O2, and O2− induced by the ultrasound catalytic ozonation (US/O3) process achieves a removal rate of 60.67 % of 5-HPA in strongly alkaline and high-salt solutions within 60 min, which is significantly higher than the O3 alone process. This technology is highly resistant to inorganic anions that coexist in industrial production, but the mineralization process is inhibited. Ozone utilization and mass transfer are significantly improved by ultrasound, including reducing the ozone bubble size by 38 %, increasing the ozone utilization rate from 52 % to 75 %, increasing the volumetric mass transfer coefficient by 61 %, and increasing the specific interfacial area by 60 %, reducing the molar ratio of ozone to TOC from 0.45 to 0.23. Through a combination of Density functional theory (DFT) and GC–MS, four pathways for removing 5-HPA are clearly proposed, which are significantly different from the evolution behavior in acidic systems. The US/O3 system has significant application potential in reducing the threat of 5-HPA to nuclear waste disposal and human health.

Continuous ultrasonic ozone coupling technology-assisted control of ceramic membrane fouling coupled enhanced multiphase mixing to treat dye wastewater and CFD flow field simulation

In this study, ozone catalysts (hydrogenation-modified red mud, HM-RM) successfully prepared by hydrogenation-modification of industrial hazardous solid waste red mud (RM) as a raw material in accordance with the viewpoint of treating waste with waste and using waste. Meanwhile, as for the common phenomenon of membrane fouling, uneven distribution of multiphase solid catalysts and ozone in liquids, the addition of ultrasound can not only disperse materials, but also play a role in online cleaning of ceramic membranes and catalysts. The optimum treatment conditions for Rhodamine B (RhB) solution with volume of 2 L and concentration of 40 mg/L were catalyst concentration of 0.4 mg/L, reaction temperature of 45 °C, ultrasonic time of 1 h, ultrasonic intensity of 600 W, removal rate of RhB was up to 90 %. In addition, the computational fluid dynamics (CFD) simulation method was used to investigate the fluid flow between the two gas-liquid phases and the effect of the negative pressure of the membrane pump on the fluid by the analysis of flow, pressure and ozone flux of the ceramic membrane(CM) reaction apparatus. The CFD simulation results showed that at the inlet gas-liquid flow rate of 3 m/s and the negative pressure of 20,000 Pa, the maximum flow rates of CM-1 were 3 m/s, 0.752 m/s for CM-2, and 0.228 m/s for CM-3, respectively. Vortices, which are beneficial to solid-liquid mixing and gas-liquid mass transfer, formed between the suction port CM-1 of CM-1 and the inlets of CM-2 and CM-3. This discovery is consistent with relevant experimental research results. Significantly higher concentrations of both •OH and dissolved ozone were observed in the US/HM-RM/O3 system compared to other systems, indicating the significant improvement in ozone utilization rate through the application of ultrasound. The superiority of the US/HM-RM/O3 device was demonstrated. The real dye effluent was tested under optimum operating conditions and the results showed that COD and TOC were reduced by 81.34 % and 60.23 % respectively after 180 min of treatment. The above research can provide technical support for the treatment of dye wastewater using Ultrasound-enhanced ozone oxidation ceramic membranes.

Enhanced Catalytic Ozonation of Phenol Degradation by Mn-Loaded γ-Al2O3 Catalyst: A Facile Strategy for Treating Organic Wastewater

Heterogeneous catalysis ozonation technology can achieve efficient treatment of refractory organics in industrial wastewater due to its advantages including fast reaction speed, high ozone utilization rate, low catalyst loss and low cost and has a broad application prospect. The development of efficient and stable heterogeneous ozone catalytic materials is the key to promoting the application of this technology in industrial wastewater treatment. Based on this, an Mn/Al2O3 catalyst was successfully prepared by impregnation method using 3~5 mm γ-Al2O3 pellets as the carrier, and the surface morphology characteristics, elemental state and phase composition of the catalyst were investigated by SEM-EDX, XRD and XPS. The results showed that Mn was successfully loaded onto the surface of a γ-Al2O3 carrier. On this basis, intermittent single factor experiments were conducted to systematically investigate the effects of catalyst dosage, pH, and ozone concentration on the catalytic performance of phenol. It was found that under the optimal conditions of a catalyst dosage of 100 g (filling height of 14.2 cm), pH of 7, and ozone concentration of 4 mg/L (gas volume of 1 L/min), the removal efficiencies of 800 mL 100 mg/L of simulated phenol wastewater reached 100% after 60 min of reaction. The removal efficiencies of the catalyst still reached 95.8% within 60 min even after the fifth cycle reaction, indicating excellent reusability of the catalyst. This work provides a facile strategy for the treatment of refractory organics in industrial wastewater.

Efficient catalytic ozonation of ethyl acetate over Cu-Mn catalysts: Further insights into the reaction mechanism

A series of Cu-Mn oxides were synthesized by the redox-precipitation method with different precipitants to evaluate the catalytic ozonation of ethyl acetate (EA). It was found that CuMn-II (with H2C2O4 as precipitant) exhibited the best catalytic activity, which achieved an EA conversion of 99 % at 120 °C with an O3/EA molar ratio of 10. The reaction temperature, O3/EA molar ratio, ozone utilization rate, and COx selectivity were also discussed. Meanwhile, many characterizations were conducted to reveal the properties of catalysts, such as SEM, XRD, BET, XPS, H2-TPR and NH3-TPD. Abundant surface defects, plentiful oxygen vacancies, larger specific surface area, higher content of Mn3+ and more acid sites contributed to the superior performance of CuMn-II. Catalyst poisoning occurred when SO2 was added, however, the conversion of EA could gradually recover to 88 % once SO2 was stopped. In-situ DRIFTS measurement was carried out to reveal the formation of intermediate species during the reaction. Combined with DFT calculations, a reaction mechanism for the catalytic ozonation of EA over CuMn2O4 catalysts was proposed.

Adsorption and catalytic ozonation of toluene on Mn/ZSM-5 at low temperature

In this study, a series of Mn/ZSM-5 catalysts with different Mn contents (2, 4, and 6 wt%) were prepared as adsorbents and catalysts. The adsorption of toluene and the regeneration performance of ozone catalytic oxidation at room temperature were investigated. The results showed that the toluene conversion reaches 90 % at 30 ℃ through 4 wt% Mn/ZSM-5 catalytic oxidation. The cycling and ozone utilization rate experiments reflected that after four consecutive adsorption-ozonation cycles, 4 wt% Mn/ZSM-5 still maintained good toluene adsorption capacity. In the regeneration process, the molar ratio of ozone consumption to toluene degradation was about 7.7:1, which was approximate to the theoretical molar ratio (6:1). The product distribution on the surface of ZSM-5 and 4 wt%Mn/ZSM-5 during toluene degradation was determined by GC-MS analysis, and possible mechanism for catalytic oxidation of toluene on the surface of ZSM-5 and 4 wt%Mn/ZSM-5 were proposed.

Interfacial mechanism of the synergy of biochar adsorption and catalytic ozone micro-nano-bubbles for the removal of 2,4-dichlorophenoxyacetic acid in water

A high-efficiency catalytic ozonation system consisting of NaOH-pretreated rice straw biochar (OHBC) and ozone micro-nano-bubbles (O3-MNBs) was developed to remove 2,4-dichlorophenoxyacetic acid (2,4-D) in water, and the interfacial mechanism was further studied in detail. The removal rate of 2,4-D was improved by 47.0% through the synergy of adsorption and catalytic ozonation in the O3-MNBs/OHBC system (89.0%) compared with the O3-MNBs alone system (42.0%), and the ozone utilization rate was increased from 0.43 mg/mg to 0.66 mg/mg. High performance for 2,4-D removal from water with diverse matrix factors could also be obtained. The many hydroxyl groups (OH) (1.25 mmol/g) on the surface of the OHBC were more powerful than the carboxyl and lactone groups (COOH and COOR) at catalyzing ozone to produce OH according to XPS and Boehm titration results. The theoretical calculations based on density functional theory (DFT) showed that ozone molecules were more readily adsorbed on the surface OH groups due to the relatively high negative adsorption energy (–0.31 eV), and they further extended the two OO bond length from 1.277 Å to 1.303 Å and 1.311 Å, thus promoting its decomposition. The degradation mechanism of 2,4-D included dechlorination, electrophilic substitution, and OH substitution, and the degraded water showed relatively low toxicity.

The Application of Ozone Micro-nano Bubble Treatment Vegetable Fresh-Keeping Technology in Air Logistics Transportation

In recent years, fresh fruits and vegetables have been sought after by Chinese people. The fresh-keeping technology, storage, and transportation of fruits and vegetables have also attracted a large number of people’s attention. Various methods of preservation, storage, and transportation of fruits and vegetables have begun to appear in the society. Micro and nanobubbles have the characteristics of long stay time, larger than the surface, high surface negative electricity, strong reliability, high efficiency of heat transfer, can cause oxygen free radicals, can greatly improve the actual effect of ozone and ozone utilization rate, and reduce the operation cost. This article aims to study the application of ozone micro-nano bubble processing vegetable fresh-keeping technology in air logistics and transportation, and put forward the idea of applying ozone micro-nano bubble processing fresh-keeping technology to fruits and vegetables fresh-keeping and transportation more widely. This article focuses on the introduction of ozone micro-nano bubbles, fresh-keeping technology, air transportation, and experiments on some fresh-keeping technologies in the article. The experimental results show that the vegetable preservation technology based on ozone micro-nano bubbles can better maintain the moisture and nutrients in the vegetables. The preservation technology of ozone micro-nano bubble treatment has improved the preservation of fruits and vegetables by 12%.

Catalytic ozonation of CH2Cl2 over hollow urchin-like MnO2 with regulation of active oxygen by catalyst modification and ozone promotion

This paper firstly reported efficient catalytic ozonation of CH2Cl2 (dichloromethane, DCM) at low temperature over hollow urchin-like MnO2 with high chlorine resistance. Regulations on morphologies and Cu doping, as well as ozone promotion were conducted to optimize active oxygen of MnO2 catalysts, contributing to excellent catalytic behaviors. Cu doping MnO2 with hollow urchin-like morphology attained a stable 100% DCM conversion with O3/DCM molar ratio of 10 at 120 °C. The ozone utilization rate, final products, and byproducts distribution were discussed. Abundant crystal defects, low-valance Mn/Cu, Oads, and weak acidity, as well as better low temperature reducibility contributed to its superior performance. During DCM catalytic ozonation, DCM oxidation exhibited competitive effect on O3 decomposition due to the occupation of intermediates (CH2ClO3·, O−CH2Cl, and O−CH2 −O) over active sites that should belong to O3 originally. Nevertheless, O3 decomposition exhibited synergistic effects on DCM oxidation with promotion on active oxygen. Density functional theory (DFT) calculations confirmed the positive effect on oxygen vacancy formation and O3/DCM adsorption from Cu doping. The possible mechanism for DCM catalytic ozonation included four parts, including O3/DCM adsorption, O3 activation, DCM oxidation, and electron replenishment. This paper provides new insight for catalytic elimination of chlorinated alkanes at mild conditions.

Cation deviated stoichiometry Ca1.1ZrO3 perovskite as an efficient ozonation catalyst for m-cresol wastewater degradation

Highly efficient and stable catalysts for continuous catalytic ozonation of organic pollutants are of great significance in industrial applications. Perovskites have been seen as promising environmental catalysts because of their tunable defect structures and electronic properties. This work reports on A-site cation stoichiometry deviation as an effective engineering strategy to improve the crystallinity of perovskite CaZrO3, as well as its catalytic ozonation activity. High pure phase Ca1.1ZrO3 nanocrystals were successfully synthesized using a co-precipitation calcination method and evaluated as ozonation catalysts for m-cresol degradation. Surprisingly, Ca1.1ZrO3 exhibits a higher total organic carbon (TOC) removal rate, ozone utilization rate, and conversion rate of m-cresol than the stoichiometric of CaZrO3 and other conventional transition metal catalysts. In addition, Ca1.1ZrO3 shows an almost constant conversion rate of m-cresol (100%) and TOC removal rate (∼82%) during uninterrupted 100-h catalytic ozonation m-cresol degradation, demonstrating its excellent catalytic stability. These outstanding catalytic activity and stability toward ozonation are attributed to the synergistic meliorated oxygen octahedron structure, including Zr cation and contiguous coordinated oxygen, by introducing a non-stoichiometry defect into the perovskite. Thus, Ca1.1ZrO3 presents an advanced oxidation process of reactive oxygen species (·OH, O2·-, 1O2). These results were verified by in situ X-ray diffraction, in situ Fourier transform infrared spectroscopy, electron paramagnetic resonance, and density functional theory. This work strongly believes that Ca1.1ZrO3 can be an efficient, stable, and an economic catalyst for catalytic ozonation.

Optimization of ozone dosage in an ozone contact tank using a numerical model.

Ozone has been widely applied in drinking water and wastewater treatment plants, and it is essential to determine the ozone dosage and its ratio in ozone contact tank to increase the ozone absorption and utilization rates. Batch experiments were performed to determine the first-order reaction rate coefficient of ozone (k1) in different raw water qualities. Results showed that k1 had an exponential decaying relationship with the ozone consumption amount (ΔO3). Based on the ozone mass transfer and decomposition kinetics, a numerical model was developed to optimize the total ozone dosage and its ratio in three aeration parts by calculating the ozone absorption and utilization rates in an ozone contact tank. The ozone absorption rate was little affected by the water quality, and an even distribution of ozone could greatly increase the ozone absorption rate. However, the ozone utilization rate was tightly related with the water quality. For waters that consumed ozone quickly, ozone should be dosed equally in three aeration parts to increase the ozone utilization rate up to 94.3%. Otherwise, more ozone should be dosed in the first aeration part. An increase in ozone utilization rate would induce an increase in the degree of water purification. This model could give theoretical support for the determination of ozone dosage and its ratio in water treatment plants rather than experience.

Decomposition of oil refinery sludge using E+-Ozonation process for carbon source releasing and TPH removal.

To utilize carbon source and decompose the petroleum hydrocarbon substances simultaneously, adding the electrolysis to ozonation (E+-Ozonation) was employed to deal with hazardous activated petroleum waste sludge (P-sludge). It was found that E+-Ozonation could accelerate the ozone utilization and hydroxyl radical (·OH) generation rate. Soluble chemical oxygen demand (SCOD) increased around 16.3 times than the control one (from 471 to 7700 mg/L). The potential carbon source, such as the short-chain carbon of acetate and propionate, increased from 50 to 1088 mg/L and from 27 to 614 mg/L respectively, and approximately accounted for a quarter of total SCOD. Total petroleum hydrocarbon (TPH) decomposition was observed with a much higher removal rate of 84.3% simultaneously, and the substances with the function group of C=C and C-C bonds decomposed greatly. The long- and medium-chain substances in TPH were converted into the short-chain substances (90% of C28-C40 of hydrocarbons was removed, while C10-C18 increased by 13.8%). E+-Ozonation process could be one of the promising methods for P-sludge decomposition through carbon source releasing and TPH removal.

Catalytic activity and evaluation of Fe-Mn@Bt for ozonizing coal chemical biochemical tail water

The purpose of this study was to improve the ozone utilization rate by preparing a high-efficiency ozone catalyst, and establish an effective model to evaluate catalytic oxidation systems. In this study, Fe-Mn@Bt ozone catalyst prepared by a doping-baking method was used to deeply treat the biochemical tail water of coal chemical wastewater. The catalyst had an extremely developed pore structure characterized by SEM. The catalytically active elements inside and on the catalyst in the form of α-Fe2O3 and MnO2 had good stability. The effects of operating conditions, such as ozone dosage, hydraulic retention time, and catalyst dosage, on total phenol and total organic carbon (TOC) removal rate were systematically investigated. Under optimal working conditions, the chemical oxygen demand (COD) after the degradation of coal chemical biochemical tail water was used as the evaluation index to explore the actual utilization rate of ozone. The addition of Fe-Mn@Bt porous catalyst upgraded the actual utilization rate of ozone from 0.14. kgCOD/kgO3 (ozone alone oxidation system) to 0.22 kg COD/kg O3. The mechanism of catalytic oxidation was investigated by adding a free radical inhibitor to a catalytic oxidation system, demonstrating that the dominant processes in a deep degradation system was that the catalysis of ozone-generated hydroxyl radicals by active elements and ozone oxidation. To further evaluate the operating conditions for Fe-Mn@Bt ozone catalyst, the “3E” evaluation system where economy, energy, and environment were the key factors was established and evaluated. At optimal levels, the removal ratios of total phenol and TOC were 58.7% and 53.5%, respectively. Fe-Mn@Bt ozone catalysts can effectively improve ozone utilization rate and has a good application prospect for the advanced treatment of coal chemical wastewater.

Performance evaluation of waste iron shavings (Fe0) for catalytic ozonation in removal of sulfamethoxazole from municipal wastewater treatment plant effluent in a batch mode pilot plant

Feasibility of iron shavings (Fe0) as a low-cost catalyst was evaluated in catalytic ozonation for degradation of sulfamethoxazole (SMX). The characterization of the catalyst studied by a variety of techniques like scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR). Experimental results indicated a first order kinetics for Fe-based catalytic ozonation (O3/Fe0) and sole-ozonation (O3) in the removal of SMX with slightly greater rate constant for O3. In the both processes, the removal efficiency of SMX was more than 99% at the first 5 min. Average COD removal efficiency in the O3/Fe0 process was about 1.36 times greater than O3. The main intermediates detected by LC-MS/MS were 3-Amino-5-methylisoxazole, benzoquinone, sulfanilic acid, hydroxyl-SMX and nitroso SMX. The mineralization of SMX significantly increased concentration of sulfate and nitrate. Fe0 enhanced ozone utilization and transfer rate. Fe0 is not requiring any preparation before use and could be a promising catalyst for practical advanced wastewater treatment.

Influence of Bi-doping on Mn1−xBixFe2O4 catalytic ozonation of di-n-butyl phthalate

Magnetic porous Bi-doping MnFe2O4 (Mn1−xBixFe2O4, x=0, 0.005, 0.01, 0.02, 0.05) were synthesized by a sol–gel method and characterized via multiple techniques. The influence of Bi-doping on catalytic ozonation of catalysts for di-n-butyl phthalate (DBP) decomposition and ozone utilization were investigated in aqueous solutions. Varying Bi-doping amount had little effect on the crystal structure, morphology and magnetism of MnFe2O4. The introduction of Bi into MnFe2O4 enhanced the catalytic DBP degradation. Hydroxyl radicals played a critical role in the Mn1−xBixFe2O4/O3 heterogeneous systems. OH generation was promoted by the surface hydroxyl groups which were regarded as main active sites of catalyst. The extent of Bi-doping had an effect on crystallite size (DXRD) and resulted in increasing surface hydroxyl site concentrations (SHSC) of catalysts. A good linear correlation between the doping amount and SHSC was observed. The initial reaction rate and DBP removal rate mainly depended on the surface hydroxyl groups in catalytic ozonation. The numbers of SHSC and average ozone utilization rate were correlated with initial reaction rates and DBP removal rates, respectively. Bi-doping not only increased the binding sites but also enhanced the tendency of ozone to decompose into OH.

The Effects of Preozonation on the Biodegradability of Phenolic Solutions Using a New Gas-Inducing Reactor

To achieve effective COD removal, the combination of preozonation with biological treatment is necessary for phenolic wastewater treatments. Preozonation of 4-cresol, 2-chlorophenol and 4-nitrophenol solutions can be carried out with high ozone utilization rate using a new gas-inducing reactor. During the preozonation, the phenolic compounds can be completely decomposed with 100% ozone utilization rate. This new gas-inducing reactor is beneficial for the preozonation of phenolic solutions, comparing with a conventional gas-liquid reactor. The BOD5 of preozonized phenolic solution is strongly related to both the degree of decomposition of phenolic compounds and the accumulation of intermediate products in aqueous solution. Based on the high ozone utilization rate, it is suggested that the optimal utilized ozone dose for 4-cresol, 2-chlorophenol and 4-nitrophenol can be chosen as 360, 350 and 400 mg/L, respectively. At those optimal utilized ozone doses, the ratio of BOD5/COD of preozonized 4-cresol, 2-chlorophenol and 4-nitrophenol solutions increase to 0.33, 0.26 and 0.33, respectively.

The effects of preozonation on the biodegradability of mixed phenolic solution using a new gas-inducing reactor

In this study, the effects of preozonation on the biodegradability of mixed 2-chlorophenol/4-cresol solution were investigated using a new gas-inducing reactor, which can provide high ozone utilization efficiency. The decomposition rate of phenolic mixture, COD removal and TOC removal increases with increasing pH. A half-order overall kinetic model can correctly describe the decomposition of phenolic mixture. The BOD 5/COD ratio of the preozonized solutions increases with increasing preozonation time, indicating that preozonation can enhance the biodegradability. Based on high ozone utilization rate, it is concluded that the best characteristic time can be chosen at the rapid increase of ozone gas outlet concentration. Since the ozone gas outlet concentration can be easily monitored, it is a useful real-time control parameter in preozonation.

The enhancement of the biodegradability of phenolic solution using preozonation based on high ozone utilization

In this research, the effects of preozonation on the biodegradability of 4-cresol, 4-nitrophenol and 2-chlorophenol solutions were investigated using a new gas-inducing reactor with high ozone utilization rate. The extent of preozonation may be monitored by determining the characteristic ozonation behaviors of preozonized phenolic solutions, such as residual phenolic concentration, ADMI value and ozone gas outlet concentration. Experimental results showed that as the initial phenolic compounds decomposed completely, the ozone gas outlet concentration rapidly increases. In addition, at pH 7, a peak ADMI value appears during the preozonation of 4-cresol and 2-chlorophenol, while for 4-nitrophenol the ADMI value decreases monotonically. Based on the characteristic ozonation behaviors and the ozone utilization rate, three characteristic times were chosen in order to have better control on the extent of preozonation. The effect of preozonation on the biodegradability of preozonized phenolic solution was studied based on these characteristic times. The intermediate products during the preozonation were also identified. The variation of BOD 5 is strongly dependent on the accumulation of intermediate products. It is suggested that the best characteristic time is as the rapid increase of ozone gas outlet concentration in this study. The biodegradability (BOD 5/COD) of preozonized 4-cresol, 2-chlorophenol and 4-nitrophenol solutions increase to 0.18, 0.26 and 0.33, respectively, for the best characteristic time.

Decolorization of Dye RB-19 Solution in a Continuous Ozone Process

This work studied the decolorization of dye C.I. Reactive Blue 19 (RB-19) solution in a new gas-inducing reactor under continuous process. The decolorization behavior, decolorization kinetic, ozone utilization rate and Chemical Oxygen Demand (COD) are examined under various operation conditions, such as input ADMI color values (ADMI o ), input liquid flow rates (Q L ), input ozone gas concentrations , input gas flow rates (Q g ), and agitation speeds (N). Experimental results of decolorization behavior indicate that the American Dye Manufactures Institute (ADMI) removal percentage ( R ADMI) decreases with increasing ADMI color value input rate or decreasing ozone input rate. For the study of ozone utilization rate, increases with increasing ADMI color value input rate or decreasing ozone input rate. The 70% ADMI removal percentage can be regarded as the index of the competition of dye and its unknown intermediates for ozone. In addition, the increase of the agitation speed can improve the ADMI removal percentage as well as the ozone utilization rate. A pseudo-first order kinetic model is adopted to describe the decolorization behavior. At steady state, the overall decolorization rate constant, k ADMIs.s., can be expressed as a function of liquid flow rate, input ADMI color value, input ozone gas concentration, gas flow rate, and agitation speed. This correlation can be used to predict the ADMI color value at steady state (ADMIs.s.) and the reactor size in the continuous process. The ΔO3/ΔCOD is dependent on the liquid composition. The higher the dye concentration in the liquid, the higher the ΔO3/ΔCOD. The COD removal percentage ( R COD) and the ozone utilization rate can be further improved by using the continuous operation with two reactors in series.